Perhaps one of the most widely used decorating techniques is piping. This can be used to create a wide variety of designs, including initials.
This technique requires a pastry bag fitted with a writing tip or a squeeze bottle with a very small opening. You can do this with frosting, royal icing, and special piping gels. If you want chocolate piping, use high-quality couverture for the best results. Melt the chocolate and place it in the pastry bag while it's still warm.
The easiest, and most popular, designs for piping are straight or diagonal lines, crosshatches, and swirls.
If you want very fine lines, choose a tip with a very small opening, make sure your piping material is very warm and fluid, and work quickly.
If you prefer heavier lines, let the material cool a bit and work more slowly, or select a tip with a slightly larger opening.
If the base glaze or coating on your dessert has not yet set, the material you pipe on top will melt into the base. If you want the decoration to sit on top of the base, wait until the base has set to decorate.
As with stenciling, if you've never piped before, practice on waxed paper.